We have demonstrated that energy restriction (40% reduction in energy consumption via reduction in fat and carbohydrate consumption) completely abolishes estrogen induction of pituitary tumors in the Fischer 344 (F344) rat. Herein are presented five specific aims designed to identify the physiological pathways and molecular mechanisms through which this occurs. Specific Aim 1 is to characterize the effect of energy restriction on the ability of 17-beta-estradiol (E2) to induce lactotroph proliferation and promote development of PRL-producing pituitary tumors in the F344 rat. The hypothesis to be tested is that energy restriction blocks pituitary tumor development in the F344 rat by inhibiting induction of lactotroph proliferation by E2. Specific Aim 2 is to determine whether or not energy restriction promotes regression of preestablished pituitary tumors. Pituitary tumors will be induced with E2 in rats fed the control diet. After 10 weeks, the animals will be fed either the control or 40% restricted diets. Tumor size and lactotroph proliferation will be examined 2 weeks later to determine if shifting from control to restricted diet induces tumor regression. Bromocriptine will be examined to determine if restriction and bromoCriptine act additively or synergistically to induce tumor regression. A potentiating effect of energy restriction on bromocriptine mediated tumor regression would suggest therapeutic potential for treatment of human prolactinoma. Specific Aim 3 is to determine if energy restriction modulates E2 regulation of genes whose protein products control lactotroph proliferation. Pituitary tissues generated in Aims I and 2 will be used to examine expression of genes encoding PRL, insulin-like growth factor, and galanin in the pituitary lactotroph. Each of these genes is regulated by E2 and their protein products regulate lactotroph proliferation. The hypothesis to be tested is: if E2 induction of one or more of these genes plays a role in tumor development. then energy restriction may inhibit this induction. Specific Aim 4 is to determine if energy restriction modulates E2 regulation of the hypothalamic/pituitary dopamine (DA) axis. We will test the hypothesis that energy restriction blocks pituitary tumorigenesis by preventing E2 from inhibiting DA synthesis by the tuberoinfundibular (TI) neurons of the hypothalamus and/or expression within the lactotroph of the gene encoding the D2 DA receptor. Specific Aim 5 is to characterize the effects of energy restriction and E2 on apoptosis in the anterior pituitary. The hypothesis to be tested is that energy restriction blocks pituitary tumor development by promoting apoptosis within the lactotroph population. An immunohistochemical assay that detects DNA fragmentation will be used to identify cells undergoing apoptosis. When coupled with immunohistochemistry for PRL, this assay will reveal the extent to which apoptosis is occurring within the lactotroph population. From this three year study will emerge a mechanistic description of how estrogens and dietary energy consumption regulate cellular processes associated with lactotroph proliferation and pituitary tumorigenesis. This knowledge may facilitate our efforts to elucidate the mechanisms through which diet influences development of other estrogen dependent human cancers.